1. Field of the Invention
The invention is directed to compatibilized polymer blends formed using a multifunctional agent in a polymer blend, preferably consisting of general purpose rubbers and benzyl halide containing polymers.
2. Related Art
Relatively saturated elastomeric polymers, such as butyl rubber, which is a copolymer of isobutylene with a small percentage of isoprene units are known. These polymers demonstrate low air permeability, relatively low glass transition temperatures, broad damping peaks, excellent environmental aging resistance, and other such properties which render these polymers of commercial significance in blends with polymers or in tire production. Butyl rubber generally is incompatible with most other polymers.
It has been known for some time that blends of incompatible polymers can be improved in some cases by adding a suitable compatibilizer so as to alter the morphology of these blends. More particularly, to be successful it has been necessary to reduce the domain sizes for both of the polymers in the blend.
It is known in some instances to use block copolymers as compatibilizers. For example, several studies have shown attempts to compatibilize rubber-rubber blends of polyisoprene and polybutadiene by using diblock materials composed of these two materials. See R. Cohen et al. Macromolecules 15, 370, 1982; Macromolecules 12, 131, 1979; J. Polym. Sci., Polym. Phys. 18, 2148, 1980; J. Macromol. Sci.-Phys. B17 (4), 625, 1980. Most of these block copolymers have been previously produced by sequential anionic polymerization processes, which are thus limited to a relatively small number of monomers. It is also known to compatibilize other blends, such as rubber-plastic blends of ethylene-propylene rubber with polypropylene, by using graft copolymers of these two materials. See A. Y. Coran et al., U.S. Pat. No. 4,299,931, as well as co-pending commonly assigned applications Ser. No. 07/264,484 now U.S. Pat. No. 4,999,403 and Ser No. 07/264,485, filed on Oct. 28, 1988.
Others have proposed different solutions for preparing compatibilized blends comprising isoolefin polymers. For example, Wang, in WO 95/09197 describes intervulcanizable blends comprising a mixture of a diolefin polymer or copolymer and a saturated or highly saturated elastomeric copolymer having a number average molecular weight of at least 10,000 and containing from about 0.01 up to about 10 mole % of xe2x80x9cYxe2x80x9d functional groups randomly distributed along and pendant to the elastomeric polymer chain, said Y functional groups containing an olefinic or vinyl double bond positioned alpha, beta to a substituent group which activates said double bond towards free radical addition reactions. The preferred activating substituent groups are carboxyl-containing groups, phosphoryl-containing groups, sulfonyl-containing groups, nitrile-containing groups, aromatic ring-containing groups or a combination of such groups.
It would be desirable to obtain a process not employing a solvent. The present invention provides compatibilized blends formed by a solventless reaction between two generally incompatible polymers with a multifunctional compound/agent.
The invention is directed to a solventless process for forming compatibilized blends of general purpose rubbers and benzyl halide polymers comprising mixing at least one general purpose rubber and a benzyl halide containing polymer in the presence of a multifunctional agent, said agent comprising a compound represented by the general formula (X)nxe2x80x94(R)mxe2x80x94(Y)p, wherein m is equal to or greater than zero, and desirably range from about 1 to about 10, n and p are greater than zero and desirably range from about 1 to about 100. X is diene reactive group. Preferably the diene reactive group is selected from the group consisting of (1) enophiles, (2) free radicals and radical traps, (3) free radical traps, and (4) nucleophiles. R is selected from the group consisting of alkyls, aryls, alkyl substituted aryls preferably having from about 1 to about 100 carbon atoms and polymers. And Y is a benzylic halogen reactive group, like a nucleophile. In addition, the present invention is also directed to using compatibilized blends of the present invention to compatibilize other polymer blends by mixing the compatibilized blend with at least one general purpose rubber and at least one polymer to form a new compatibilized blend.
The invention is further directed to a compatibilized blend of general purpose rubbers and benzyl halide containing polymers comprising mixing general purpose rubbers, benzyl halide containing polymers and a multifunctional agent comprising a compound having the formula (X)nxe2x80x94(R)mxe2x80x94(Y)p, wherein m is equal to or greater than zero, n and p are greater than zero, X is a diene reactive group, R is selected from the group consisting of alkyls, aryls, alkyl substituted aryls having from about 1 to about 100 desirably 1-20 carbon atoms and polymers, and Y is a benzylic halide reactive group. In addition, the present invention is directed to the cured compatibilized blends described above.
The present invention is directed to compatibilized blends of general purpose rubbers (xe2x80x9cGPRxe2x80x9d) and benzyl halide containing polymers. The present invention is also directed to a process for the production of compatibilized blends of GPR and benzyl halide containing polymers. Moreover, the present invention is directed to compatibilized blends of GPR and poly(isobutylene-co-methylstyrene) containing 4-halomethylene units (hereinafter BIPMS) disclosed in U.S. Pat. No. 5,162,445, herein incorporated by reference. The present invention is further directed to a solventless process for the production of compatibilized blends of GPR and BIPMS. In addition, the present invention is directed to utilizing compatibilized blends of the present invention to compatibilize other polymer blends.
In a particularly preferred embodiment, the compatibilized blends of the present invention are comprised of a blend of general purpose rubbers and BIPMS. The benzyl halide copolymers are desirably elastomeric copolymers of isobutylene, a para-methyl styrene containing from about 0.5 to about 20 mole percent para-methyl styrene wherein up to about 60 mole % of the methyl substituent groups present on the aromatic ring contain a bromine or chlorine atom. These copolymers and their method of preparation are disclosed in U.S. Pat. No. 5,162,445, hereby incorporated by reference. The blends of the present invention may include but are not limited to the following general purpose rubbers: natural rubber (NR), polyisoprene (IR), polybutadiene (BR), poly(styrene-co-butadiene) (SBR), and poly(acrylonitrile-co-butadiene) (NBR).
Generally, the blends of the present invention may comprise from about 5 to about 95 percent by weight GPR and from about 5 to about 95 percent by weight benzyl halide containing polymer. Preferably the blends comprise from about 15 to about 85 percent by weight GPR and from about 15 to about 85 percent by weight benzyl halide containing polymer. Most preferably, the blends of the present invention are comprised of about 30 to about 70 percent by weight GPR and from about 30 to about 70 percent by weight benzyl halide containing polymer. The multifunctional agent employed in the practice of the present invention generally comprises from about 0.01 to about 10 percent by weight, preferably 0.01 to about 3 percent, of the total blend weight.
The process of the present invention may be carried out in a single step or in two steps. For example, the multifunctional agent may be mixed with the GPR or the benzyl halide polymer first and then added to the other component with mixing and heating. Alternatively, the process of the present invention may be carried out in a single pass or step wherein the multifunctional agent, GPR, and benzyl halide polymer are mixed and heated together simultaneously.
Utilizing either process described above, the reaction is conducted under solventless conditions using internal mixers, extruders, and rubber milling equipment. Typical mixers include Brabender(trademark) and Banbury(trademark) mixers. As stated above, the rubber compositions are placed in the mixers along with the multifunctional agent and reacted under shear and heat to yield the compatibilized blends of the present invention.
The multifunctional agent of the present invention is a multifunctional compound containing both a diene reactive group and a benzyl halide reactive group. The multifunctional agent of the present invention has the following formula: (X)nxe2x80x94(R)mxe2x80x94(Y)p, wherein m is equal to or greater than zero, and n and p are equal to or greater than one. X is a diene reactive group and may be selected from the group consisting of (1) enophiles, (2) free radicals and free radical traps, (3) free radical traps and (4) nucleophiles. The enophiles which are useful in the practice of the present invention include, but are not limited to, maleic anhydride and its activated derivatives, including but not limited to carboxy maleic, sulfo maleic, methyl maleic, and phenyl maleic, etc., as well as the analogous nitrogen species, triazolinediones. The free radical sources useful in the practice of the present invention include, but are not limited to, peroxides, azo compounds, and polymer bond cleavage, i.e., radicals formed during GPR mastication. Preferred peroxides include dicumyl peroxide, di-t-butyl peroxide, benzoyl peroxide, bis p-chlorobenzoyl peroxide, and t-butyl cumyl peroxide. Preferred azo compounds include 2,2xe2x80x2-azo bis(isobutyronitrile); 1,1xe2x80x2-azo bis(cyclohexanecarlonitrile); 4,4xe2x80x2-azo bis(4-cyanovaleric acid); and 2,2xe2x80x2-azo bis(2-amidinopropane).
The radicals can either add to the olefin or extract a proton leading to polymeric radicals. These radicals can be trapped using suitable radical sinks or traps, e.g., sulphides, sulphenylchlorides, and thioacids. Alternately, the radicals can be trapped utilizing free-radical polymerizable monomers, e.g., acrylic, and methacrylic acid.
Y is the benzylic halide reactive group and is a nucleophile. Preferably, the nucleophilic groups which are useful in the practice of the present invention include, but are not limited to carboxylates, amines, phosphines, alkoxides, phenoxides, and thiolates.
R may be an alkyl, aryl or an alkyl-substituted aryl containing from about 1 to about 100 carbon atoms, or a polymer having a Mw up to about 100,000. Polymers which are suitable as R may be prepared by controlled polymerization methods such as xe2x80x9clivingxe2x80x9d anionic, cationic, or free-radical reactions. These xe2x80x9cliving polymersxe2x80x9d are conveniently prepared by contacting the monomers or combination of monomers with a polymerization initiator in the presence of an inert organic diluent which does not participate in or interfere with the polymerization reaction. For example, dimethylaminopropyllithium may be used to initiate the xe2x80x9clivingxe2x80x9d polymerization of dienes like butadiene and isoprene. This xe2x80x9clivingxe2x80x9d chain is then terminated with propylene sulfide. The polymer thus has an end which can react with benzylhalide and a second end which is diene reactive. Alternatively, polymers suitable as R may be obtained by ring-opening polymerization of cyclic monomers using a suitable functionalized initiator. The molecular weight of the R polymer may vary depending upon the application; however, typically polymers desirably having a molecular weight ranging from about 500 to about 100,000 are useful in the practice of the present invention.
The compatibilized blends of the present invention may be cured generally using curing systems known in the rubber industry. For example, curing systems useful in curing the blends of the present invention include but are not limited to systems comprising sulfur compounds, zinc compounds, metal compounds, radical initiators, etc. Specific compounds useful as curatives in the present invention include, but are not limited to, zinc oxide, stearic acid, tetramethylthiuram disulfide (TMTD), 4,4xe2x80x2-dithiodimorpholine (DTDM), tetrabutylthiunram disulfide (TBTD), benzothiazyl disulfide (MBTS), hexamethylene-1,6,-bisthiosulfate disodium salt dihydrate (ERP 390), 2-(morpholinothio) benzothiazole (MBS or MOR), blends comprising 90% by weight MOR and 10% by weight MBTS (MOR90), N-oxydiethylene thiocarbamyl-N-oxydiethylene sulfenamide (OTOS) zinc 2-ethyl hexanoate (2EH); and MC sulfur.
The present invention, while not meant to be limited by, may be better understood by reference to the following examples.